Julian J.C. Dawson

Assessing the influence of compost and biochar amendments on the mobility and toxicity of metals and arsenic in a naturally contaminated mine soil.

Amending contaminated soils with organic wastes can influence trace element mobility and toxicity. Soluble concentrations of metals and arsenic were measured in pore water and aqueous soil extracts following the amendment of a heavily contaminated mine soil with compost and biochar (10% v:v) in a pot experiment. Speciation modelling and toxicity assays (Vibrio fischeri luminescence inhibition and Lolium perenne germination) were performed to discriminate mechanisms controlling metal mobility and assess toxicity risk thereafter. Biochar reduced free metal concentrations furthest but dissolved organic carbon primarily controlled metal mobility after compost amendment. Individually, both amendments induced considerable solubilisation of arsenic to pore water (>2500 μg l(-1)) related to pH and soluble phosphate but combining amendments most effectively reduced toxicity due to simultaneous reductions in extractable metals and increases in soluble nutrients (P). Thus the measure-monitor-model approach taken determined that combining the amendments was most effective at mitigating attendant toxicity risk.

Biodegradability of natural dissolved organic matter collected from a UK moorland stream

The fate of dissolved organic matter (DOM) exported from headwaters is a large uncertainty in global carbon models and catchment biogeochemical process understanding. We examined the biodegradability of stream DOM collected during different flow conditions (n = 12) from a heather-dominated moorland headwater in NE Scotland. Freeze-dried DOM isolates were characterised, re-dissolved to 10 mg C L(-1), inoculated with indigenous stream sediment microbes and incubated, with and without added nutrients, to assess decomposition rates at different times up to 41 days. Biodegradable DOM ranged from 5.0 to 19% of the total transported DOM, representing 8.54 kg C ha(-1) yr(-1) (11.1% of the total DOC flux, calculated as 77.2 ± 39.0 kg C ha(-1) yr(-1)). No simple patterns with flow rate were apparent but accumulated antecedent rainfall, specific UV absorbance of DOM and (15)N content were significant predictors of the proportion of organic matter decomposed. In headwater streams draining organic-rich catchments, in-stream DOM decomposition processes act as a secondary control on the spatial variability of carbon species, and are important for establishing accuracy of aquatic carbon fluxes and cycling budgets. Moreover, biologically-mediated DOM decomposition represents a net climate forcing effect via the soil-stream-atmosphere pathway, drives downstream ecosystem metabolism and should be incorporated in carbon predictive modelling and ecosystem process studies.

Evaluation of spot and passive sampling for monitoring, flux estimation and risk assessment of pesticides within the constraints of a typical regulatory monitoring scheme

In many agricultural catchments of Europe and North America, pesticides occur at generally low concentrations with significant temporal variation. This poses several challenges for both monitoring and understanding ecological risks/impacts of these chemicals. This study aimed to compare the performance of passive and spot sampling strategies given the constraints of typical regulatory monitoring. Nine pesticides were investigated in a river currently undergoing regulatory monitoring (River Ugie, Scotland). Within this regulatory framework, spot and passive sampling were undertaken to understand spatiotemporal occurrence, mass loads and ecological risks. All the target pesticides were detected in water by both sampling strategies. Chlorotoluron was observed to be the dominant pesticide by both spot (maximum: 111.8ng/l, mean: 9.35ng/l) and passive sampling (maximum: 39.24ng/l, mean: 4.76ng/l). The annual pesticide loads were estimated to be 2735g and 1837g based on the spot and passive sampling data, respectively. The spatiotemporal trend suggested that agricultural activities were the primary source of the compounds with variability in loads explained in large by timing of pesticide applications and rainfall. The risk assessment showed chlorotoluron and chlorpyrifos posed the highest ecological risks with 23% of the chlorotoluron spot samples and 36% of the chlorpyrifos passive samples resulting in a Risk Quotient greater than 0.1. This suggests that mitigation measures might need to be taken to reduce the input of pesticides into the river. The overall comparison of the two sampling strategies supported the hypothesis that passive sampling tends to integrate the contaminants over a period of exposure and allows quantification of contamination at low concentration. The results suggested that within a regulatory monitoring context passive sampling was more suitable for flux estimation and risk assessment of trace contaminants which cannot be diagnosed by spot sampling and for determining if long-term average concentrations comply with specified standards.

Evaluating the use of in - situ turbidity measurements to quantify fluvial sediment and phosphorus concentrations and fluxes in agricultural streams

Accurate quantification of suspended sediments (SS) and particulate phosphorus (PP) concentrations and loads is complex due to episodic delivery associated with storms and management activities often missed by infrequent sampling. Surrogate measurements such as turbidity can improve understanding of pollutant behaviour, providing calibrations can be made cost-effectively and with quantified uncertainties. Here, we compared fortnightly and storm intensive water quality sampling with semi-continuous turbidity monitoring calibrated against spot samples as three potential methods for determining SS and PP concentrations and loads in an agricultural catchment over two-years. In the second year of sampling we evaluated the transferability of turbidity calibration relationships to an adjacent catchment with similar soils and land cover. When data from nine storm events were pooled, both SS and PP concentrations (all in log space) were better related to turbidity than they were to discharge. Developing separate calibration relationship for the rising and falling limbs of the hydrograph provided further improvement. However, the ability to transfer calibrations between adjacent catchments was not evident as the relationships of both SS and PP with turbidity differed both in gradient and intercept on the rising limb of the hydrograph between the two catchments. We conclude that the reduced uncertainty in load estimation derived from the use of turbidity as a proxy for specific water quality parameters in long-term regulatory monitoring programmes, must be considered alongside the increased capital and maintenance costs of turbidity equipment, potentially noisy turbidity data and the need for site-specific prolonged storm calibration periods.

Loss of Soil Carbon to the Atmosphere via Inland Surface Waters

Within the global carbon (C) cycle, there is still much debate as to the magnitude, location and turnover of the terrestrial C sinks (and sources). One of the major keys to closing this knowledge gap is that globally, the amount of C entering oceans maybe only ca. 33 % of the total C transported from terrestrial ecosystems to inland surface waters. Streams, lakes, rivers and transitional waters are areas for the active transformation and recycling of terrestrially-derived C indirectly back to the atmosphere (estimated range of 25–44 %). Understanding processes that control soil C losses to and its fate in surface waters is not only important in establishing accuracy of C fluxes, feedbacks and tradeoffs but also providing evidence to limit terrestrial ecosystem C contributions to atmospheric carbon dioxide (CO2).

The potential use of natural vs commercial biosorbent material to remediate stream waters by removing heavy metal contaminants

The presence of high level of heavy metals in aquatic environment is a cause of ecological and environmental concern and thus their removal from water courses is environmentally essential. Four natural inexpensive biosorbents: macro algae (Fucus vesiculosus), crab shells (Cancer pagurus), wood chippings and iron-rich soil were tested for copper (Cu2+) and zinc (Zn2+) removal from aqueous solutions. Batch equilibrations were performed at 1:100 w/v with different initial metal concentrations. Three macro algae pre-treatments (unmodified (UM algae), chemically treated (Ca-T algae) and thermally treated (T-T algae)) were additionally investigated for performance. The sorption capacities were compared with the commercial material biochar and activated carbon. The maximum level of the sorbents for Cu2+ uptake at 15.7u202fmM/l was attained by the natural material of UM algae (72.37u202f±u202f0.37u202fmg/g)u202f>u202fCa-T algae (66.77u202f±u202f0.19u202fmg/g)u202f>u202fT-T algae (63.06u202f±u202f0.82u202fmg/g), followed by the commercial material activated carbon (36.71u202f±u202f2.20u202fmg/g). The maximum level of the sorbents for Zn2+ uptake at 15.3u202fmM/l was also achieved by the natural material of UM algae (52.40u202f±u202f0.80u202fmg/g)u202f>u202fCa-T algae (48.83u202f±u202f2.01u202fmg/g)u202f>u202fT-T algae (39.57u202f±u202f0.80u202fmg/g) followed by the commercial material activated carbon (20.78u202f±u202f1.63u202fmg/g) and biochar (18.07u202f±u202f1.09u202fmg/g). The results demonstrated that Cu2+ and Zn2+ were effectively removed by these biosorbents at all concentrations. However, at high metals concentrations, the natural material macro algae had greater Cu2+ and Zn2+ sorption capacity than the conventional sorbent activated carbon, and the affinity of these natural biosorbents were greater for Cu2+ than Zn2+. Hence, inexpensive natural and readily available materials showed potential as biosorbents to remediate polluted stream water of toxic metal contaminants.